Fixed casper.getPageContent() for Gecko

Gecko encloses non HTML content in an HTML web page, like Webkit,
but with some differences.
Tests & Gecko: fixed error about createDocument in utils.js

The third parameter is mandatory in Gecko 25 and lower. It
is optional since Gecko 26 (not released yet at that time)
Reactivate some tests about http status for PhantomJS 1.9.2+
Add CSS selector support to assertField
Add documentation for ClientUtils.log()
Merge pull request #709 from clochix/patch-3

Add documentation for ClientUtils.log()
Fixed jshint issues
Add docs and throw exception when type is invalid, test coverage
Merge pull request #706 from mduvall/assert-field-css-selector-redux

Add CSS selector support to assertField
fixes 711 - proper cli arguments parsing
refs #594 - added slimerjs to travis build matrix
updated engine archive download strategy in matrix config
updated python test runner to use ENGINE_EXECUTABLE
Merge pull request #714 from n1k0/add-slimer-to-travis-build

Added slimerjs to travis build matrix - refs #594
separated dotNET tests from others in travis config
Merge pull request #716 from n1k0/travis-matrix-dotnet-config

Separated dotNET tests from others in Travis config
fixed elem visibility computation method - refs #715
refs #717 - fixed typo in readme

correct misspelled 'bootsrap' to 'bootstrap'
Fix #717
refs #711 - better cli arguments parsing

fixes regression introduced by 8b41b70055f43e2e004951762472fb3af0235305
Merge pull request #718 from phillipalexander/fix-readme-typo

refs #717 - fixed typo in readme